Anodizing is a common method of providing an anodic oxide coating on a metal substrate, often used in industry to provide a protective and sometimes cosmetically appealing coating to metal parts. During an anodizing process, a portion of the metal substrate is converted to a metal oxide, thereby forming a protective oxide layer or coating. The nature of the anodic oxide coatings can depend on a number of factors, including chemical makeup of the metal substrates and the process parameters used in the anodizing processes. Anodizing can be a particularly useful technique to preserve surface finishes on the exterior of a consumer device, particularly with respect to soft metals that scratch or dent easily, such as aluminum.
Titanium is a relatively hard metal for which anodizing to create a protective layer is not common, however, since a typical oxide layer forming at a titanium surface tends to be too thin to provide much protection. Rather, titanium and its alloys are often subjected to nitriding, carburizing, carbo-nitriding, nitro-carburizing, or similar processes in order to harden its surfaces to provide a protective surface finish, which can be extremely hard and ceramic in nature. These processes are also sometimes used for cosmetic purposes, since they can sometimes result in color changes. For example, the gold appearance of titanium nitride is often selected for cosmetic reasons. These processes can be limiting, however, and it is generally not common for a very hard nitrided or carburized titanium surface to be further treated in a cosmetic manner.
While metal surface finish processes are known to have worked well in the past, there can be room for improvement. Accordingly, there is a need for improved systems and methods that provide durable and aesthetically pleasing metallic surface finishes for consumer devices.